1. Field of the Invention
The present invention relates to an internal-gear type fluid device that includes an outer rotor and an inner rotor.
2. Description of the Related Art
A fluid motor in which an inner rotor is driven using a pumped fluid and a fluid pump in which an inner rotor is driven to discharge a fluid have been disclosed as internal-gear type fluid devices that include an outer rotor and an inner rotor. For example, the fluid pump has a plurality of pumping chambers between the outer rotor and the inner rotor, and the volume of each chamber is increased or decreased by rotating the inner rotor, thereby pumping a fluid such as oil from an intake port to a discharge port.
In such a fluid pump, the volume of the pumping chamber decreases following the rotation of the rotor even after the fluid has been confined in the pumping chamber, thereby causing an excessive increase in the pressure inside the pumping chamber. When the pumping chamber thereafter communicates with the discharge port, the pressure inside the pumping chamber drops rapidly, and, therefore, cavitation occurs inside the pumping chamber. The cavitation causes noise and vibrations and decreases the pumping efficiency.
Accordingly, a fluid pump has been disclosed (see, for example, Japanese Unexamined Patent Application Publication No. 2005-188380) in which cutouts are formed in the teeth surfaces of the outer and inner rotors, and the pumping chambers are communicated via the cutouts, thereby causing the fluid to move between the pumping chambers. As a result, pressure fluctuations inside the pumping chambers are inhibited and the occurrence of cavitation is suppressed.
However, in the fluid pump described in Japanese Unexamined Patent Application Publication No. 2005-188380, although the pumping chambers are communicated with one another via fine cutouts, the pumping chamber volume decreases from the confinement of the fluid has been completed to the release of the fluid. Such a decrease in the pumping chamber volume before the fluid is released to the discharge chamber causes an excessive increase in pressure, and therefore, the occurrence of cavitation is difficult to prevent.